The present invention relates to an apparatus and method for forming fibers from molten thermoplastic fiberizable materials, and in particular, to an apparatus and method for forming fibers from molten thermoplastic fiberizable materials which improves the physical characteristics of the fibers produced and the integrity of blankets formed from the fibers.
Rotary fiberizing processes typically include a rotating fiberizing disk with an annular peripheral sidewall containing rows of fiberizing holes. The rotating fiberizing disk is supplied by a stream of hot molten thermoplastic fiberizable material, such as but not limited to glass, which is deposited on a bottom wall of the fiberizing disk inwardly of the disk sidewall. The centrifugal force produced by the rotation of the fiberizing disk causes the hot, molten fiberizable material to flow across the bottom wall of the fiberizing disk and up the disk sidewall where the hot, molten fiberizable material passes out through the fiberizing orifices to form fibers.
In a first form of the process, an annular combustion burner is located concentrically relative to the fiberizing disk which is typically about 12 inches to about 18 inches in diameter. The annular combustion burner discharges hot, high velocity combustion gases from its internal combustion chamber downward into an annular region adjacent and surrounding the disk sidewall to form a heated fiber attenuation zone for attenuating fibers issuing generally horizontally from the fiberizing holes in the disk sidewall. At and adjacent the uppermost row of fiberizing holes in the fiberizing disk sidewall, the velocity of the combustion gases of the hot, high velocity annular flame typically ranges from about 500 feet per second to about 700 feet per second. These hot, high velocity combustion gases a) envelope the fibers as the fibers issue from the fiberizing orifices to maintain the fibers issuing from the fiberizing holes in a softened state as the fibers pass through the heated fiber attenuation zone; b) pull on the fibers issuing from the fiberizing holes to attenuate the fibers as the fibers pass through the heated fiber attenuation zone; and c) redirect the fibers downward. After the redirected fibers pass from the heated attenuation zone, the fibers solidify and are collected. Typically, the energy input at the fiberizer required by this process to produce one pound of glass fibers (the energy from the molten glass and the attenuating flame of the external attenuation burner) ranges from about 2500 to about 3300 British Thermal Units (BTU's).
In a second form of the process, a manifold delivers an air/gas mixture (typically an air/natural gas mixture) internally of the fiberizing disk and an annular air ring is located concentrically relative to and spaced outwardly from the fiberizing disk. In this form of the process the fiberizing disk is typically about 15 inches to about 30 inches in diameter. The air/gas mixture, introduced into the fiberizing disk, is gas rich (fuel rich) whereby the air/gas mixture not only combusts within the fiberizing disk but unburned gas from the mixture spills over the outer rim and passes generally downward along the peripheral sidewall of the fiberizing disk where the gas burns adjacent the sidewall and forms a heated fiber attenuation zone adjacent and surrounding the fiberizing disk sidewall. Thus, the combustion of the air/gas mixture introduced into the fiberizing disk, within the fiberizing disk, maintains the fiberizing disk and the molten fiberizable material within the fiberizing disk within a selected or desired temperature range for fiberization and the combustion of the unburned gas spillover from the air/gas mixture adjacent and surrounding the disk sidewall produces a heated fiber attenuation zone where fibers issuing generally horizontally from the fiberizing holes in the disk sidewall are attenuated. At and adjacent the uppermost row of fiberizing holes in the fiberizing disk sidewall, the velocity of the combustion products from the combustion of the fuel spillover typically ranges from about 20 feet per second to about 50 feet per second. The air ring discharges a high velocity (typically about 1,000 feet per second and higher) curtain of air in a downward direction to pull on and attenuate the fibers as the fibers pass through the heated fiber attenuation zone and solidify and redirect the fibers downward for collection after the fibers have passed through the heated fiber attenuation zone. Typically, the energy input at the fiberizer required by this process to produce one pound of glass fibers (the energy from the molten glass, from the combustion of the air/gas mixture within the fiberizing disk, from the combustion of the gas spillover, and from air curtain) ranges from about 1,000 to about 1,700 British Thermal Units (BTU's).
While both of these processes are in commercial use and function quite satisfactorily to produce commercially acceptable grades of fibers (e.g. glass fibers), there has remained a need to produce fibers of equal or better quality at energy consumptions equaling or approximating the energy consumption of the second process rather than the first process discussed above e.g. energy consumptions of about 1,000 to about 1700 BTU's per pound of glass fibers produced vs energy consumptions of about 2,500 to about 3,300 BTU's per pound of glass fibers produced.